M系列相関法による板中の曲げ波伝搬の測定
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概要
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M-sequence correlation method is applied to the measurement of flexural wave propagation in a plate. Transfer function G(s) between two points in a wave propagating system is considered. If G(s) has the form of (5), the relation between input and output signals is derived as (6), and group delay τ_<gj> and amplitude coefficient κ_j can be measured by M-sequence correlation method as (14). Experiments were performed to measure the flexural wave on a long thin steel strip and two wave components were obtained as shown in Fig. 2. The group velocity of the fast wave component is plotted in Fig. 3, which can be explained by conventional one dimensional beam theory. To explain the slow wave component, flexural wave propagation in a two dimensional plate was analysed. General solution (17) of the wave equation was assumed and parameters in it were determined from free edge boundary condition. Characteristic equation (25) was derived by assuming the presence of non-zero solution and it was solved by an electronic computer. There exist two kinds of waves, one is the zeroth order wave which is shown in Fig. 7 and the other is the first order shown in Fig. 10. The zeroth order wave consists from infinite components 01, 02, 03・・・, and the first order wave is very similar to the wave obtained by one dimensional conventional beam theory. From group velocities, mode shapes and cutoff frequencies it is supposed that the fast wave component measured in experiments is the first order wave and the slow wave component is the 02 order wave.
- 1973-06-01